The Experts below are selected from a list of 3396 Experts worldwide ranked by ideXlab platform
P Trapper - One of the best experts on this subject based on the ideXlab platform.
-
Numerical analysis of offshore pipe-Lay subjected to environment-induced non-uniformly distributed follower loads
Applied Ocean Research, 2020Co-Authors: P Trapper, Idan MishalAbstract:Abstract The global pipeline configuration in installation is mainly governed by static Lay effects, which, besides pipeline material properties and geometry, primarily depend on its submerged gravity and horizontal Tension provided by the Laying vessel. These loads are insensitive to the pipeline deformation and preserve both their values and their directions as the pipeline deforms throughout the whole course of the installation. However, these static Lay effects may be significantly amplified by the environmental factors, primarily caused by astronomical ocean tides, such as water level variations and hydrodynamic currents. These factors may substantially affect pipeline configuration and significantly increase the internal forces. Moreover, the loads caused by the ocean currents are of a fundamentally different nature comparing to the gravity and the Lay Tension. They are nonuniformly distributed along the pipeline axis and change both their values and their directions following the nonlinear deformation of the pipeline throughout the course of the Laying process. This paper presents a feasible numerical method for a structural analysis of a pipeline static configuration in installation, subjected to non-uniformly distributed, position- and orientation-dependent loading and water level variations. The method considers the whole pipeline, which is partially suspended and partially laid-on a seabed, as a single continuous segment, and is valid for both S-Lay and J-Lay techniques. The numerical solution adopts finite difference discretization of the pipeline, and proceeds sequentially in an incremental way, following the actual pipe-Lay process. At each length increment a new consequent equilibrium configuration is being assessed by consistent minimization of the updated total potential energy, which allows for considering follower loads, which change both their values and their directions following the nonlinear deformation of the pipeline. Representative parametric study is conducted to demonstrate the feasibility of the method. Considered the effects of a power-law current velocity depth-varying profile and water level variations. The method compared to Abaqus/AQUA and its convergence is validated through finite difference grid refinement. The proposed technique presents a less time-consuming alternative to the available special-purpose commercial software that imposes the use of cumbersome Graphical User Interface for a model definition and a result processing.
-
Static analysis of offshore pipe-Lay on flat inelastic seabed
Ocean Engineering, 2020Co-Authors: P TrapperAbstract:Abstract Pipeline embedment into a seabed has a great effect on its integrity during its installation and operation. To assess the embedment accurately, inelastic behavior of the seabed should be considered. This paper presents feasible numerical model for the analysis of a pipeline, umbilical or cable configuration in installation on inelastic seabed, capturing irreversible embedment. The model considers the entire pipeline as a single continuous segment, and is valid for S-Lay, J-Lay and reel-Lay techniques. The numerical solution adopts finite difference discretization of the pipeline, and proceeds sequentially following actual pipe-Lay process, allowing for an efficient contact detection. At each length increment a new consequent equilibrium configuration is assessed by consistent minimization of a total potential energy, which allows considering non-conservative and path-dependent systems. Representative parametric study is performed to demonstrate the feasibility of the method. The effects of seabed loading and unloading stiffnesses for varying Lay Tension are considered. The parameter analysis has revealed that accepted static touchdown Lay factor should depend on a seabed loading stiffness in a non-monotonic manner. The proposed model provides a less time-consuming alternative to the available special-purpose commercial software that imposes the use of cumbersome Graphical User Interface for model definition and result processing.
-
feasible numerical method for analysis of offshore pipeline in installation
Applied Ocean Research, 2019Co-Authors: P TrapperAbstract:Abstract Feasible numerical method for a structural analysis of a pipeline configuration during the installation process is presented. The method considers the whole pipeline, which is partially suspended and partially laid-on a seabed, as a single continuous segment, and is valid for a complete range of Laying angles between 0°–90°, i.e., valid for both S-Lay and J-Lay configurations. The method accounts for a pipeline–seabed interaction and the pipeline is modeled by means of nonlinear large deformation beam theory. The numerical solution is carried out in an incremental-iterative manner by following the actual pipeline installation process, and thus allowing efficient treatment of pipeline-seabed interaction circumventing the further complexities with contact detection. At each increment, the length of the pipeline is increased and new sequential equilibrium configuration is assessed by direct minimization of a total potential energy approximated as a Riemann sum, which yields algebraic system of nonlinear finite difference equations that is further solved by iterations with Newton-Raphson technique. The simplicity, flexibility and robustness of the proposed method allow to enhance the efficiency of engineering calculations and design. Accounting for a bending stiffness in a suspended part allows analyzing variations in Laying angle and Lay Tension independently. The method convergence is validated and compared with Abaqus. The results are in an excellent agreement. Moreover, the comparison with Abaqus shows that for the selected parameters the assumption that the pipeline is inextensible and unshearable is very reasonable. Representative parametric study is conducted to demonstrate the feasibility of the method. Parametric study considers the effects of Laying angle (0°–90°), Lay Tension, Laying water depth (up to 3000 m) and seabed stiffness.
Joakim Nyman - One of the best experts on this subject based on the ideXlab platform.
-
Global buckling of subsea pipline on uneven seabed.
2014Co-Authors: Joakim NymanAbstract:Exposed subsea pipelines operating under high pressure and high temperature may experience a phenomena known as global buckling. Global buckling can be described as an extensive transversal movement of the pipeline once the critical load is reached. Although that global buckling is not a failure mode itself it may lead to other failure modes such as local buckling.This master thesis aims to investigate the global buckling phenomena of exposed subsea pipeline in order to create a parametric 3D Finite Element (FE) model in ANSYS and a post processing script in Python for global buckling analyses according to Den Norske Veritas (DNV) standards. To do this, two FE-analyses are performed, the first one for verifying the ANSYS FE-model setup and the second one to evaluate the parametric 3D FE-model for global buckling on uneven seabed. The verification is carried out on a 10 km long pipeline resting on even seabed with a geometrical imperfection and is compared with an analytical solution. This, in order to verify the FE-model setup before it is used in a more complex model with an uneven seabed. The comparison is performed for two different sizes of initial imperfection amplitudes and two different set of orthotropic friction parameters.The parametric 3D FE-model in ANSYS is developed according to offshore standard for global buckling, DNV-RP-F110. A 4 km long gas injection pipeline section is analyzed for different functional loads where the pipeline and the seabed is implemented from real routing coordinates. The pipeline is modeled by first order pipe element and the seabed with 4-node target elements. The pipeline initially is resting on link elements, only active in compression, to simplify the installation of the pipeline and is thereafter removed. To be able to describe the orthotropic friction, including lateral break-out-resistance, is three contact elements applied on each pipe element. An elasto-plastic material model including derating effects of the material parameters caused by temperature effects is used for the pipeline. A result post processing script is developed to evaluate the result and determine the utilization according to thecombined load criterion for local buckling in DNV-OS-F101.The verification study results show a large difference for very small deformations where the FE-model is softer than the analytical model. This is caused by the analytical solution not considering pre-buckling. After the pre-buckling the FE-model is stiffer than the analytical model which probably is due to the update of the element stiffness matrix for each iteration in the FE-model. Although the large errors in the pre-buckling region the FE-model setup can be considered as valid. The result for the gas injection pipeline shows two lateral buckles, one mode four and one mode three, where the bends in the route act as initiators. Several vertical buckles are also obtained and they are located in free spans where the sag of the pipeline is acting as initiator. The utilization of the pipeline according to the combined load criterion is below required according to DNV-standard for all load cases and no further modification of the pipeline is needed regarding the local buckling. When evaluating the parametric 3D global buckling FE-model it was concluded that converge problems mainly arise from the installation phase. The model is sensitive to large global slopes and large magnitudes of unevenness of the seabed and may result in convergence problems. In those cases, an adjustment in the pipeline installation angle is required to achieve convergence. Furthermore, the multiple contact on each pipeline element for describing the lateral break-out-resistance increases the computational time. An implementation of a new friction model which describes the lateral friction as function of lateral sliding displacement would improve the performance of the model. Besides the convergence issue was the response of the evaluation satisfying and no unphysical behavior in the response could be observed. However, in the FE-model Lay Tension is introduced after installing the pipeline and may be a source of error, further investigations in this area is recommended.
Antonio Pereira - One of the best experts on this subject based on the ideXlab platform.
-
On the Challenges With Pipeline Free Spans in Operational Phase
Volume 6A: Pipeline and Riser Technology, 2014Co-Authors: Celso Raposo, Olav Fyrileiv, Antonio PereiraAbstract:Free span assessment has more and more become an important part of modern pipeline design. The reason for this is partly that the remaining hydrocarbon reservoirs are located in more challenging places, e.g. with very uneven seabed. Another explanation is that the pipeline design codes a few decades ago did not allow for vibrating free spans, while the modern, state-of-the-art pipeline codes, such as DNV-OS-F101 “Submarine Pipeline Systems” (2013) and its Recommended Practices, opens for long spans that are allowed to vibrate as long as the structural integrity is ensured.In presence of non-cohesive soils and high on-bottom flow velocities significant free span development may occur over the design life, e.g. due to scouring. Such spans may be associated with a fatigue life capacity less than the design life if the spans are assumed stationary. For non-stationary spans with occasional long span lengths this may not be true since the criticality is strongly linked to the persistence of long spans and the prevailing environmental condition. A realistic fatigue assessment must account for the history of the span (i.e. stress cycles encountered for a critical weld) including predictions into the future development.High costs related to span intervention puts focus on minimizing these costs while still ensuring integrity of the pipeline with respect to vortex induced vibrations (VIV) and associated fatigue damage. On the other hand the potential costs related to fatigue failure of a pipeline (recovery costs, economical loss and environmental consequences) are enormous. Therefore it is essential to ensure that the probability of failure for free spans is within acceptable limits.One frequent challenge faced with old pipelines in operations survey reports are that they report several free spans. Old pipelines were not designed to allow any vibration and usually there is scanty information about different parameters such as soil conditions, operational parameters, Lay Tension, environmental data, etc., thus it’s difficult to determine whether it’s necessary to intervene the span or not.State-of-the-art free span codes are deterministic in their nature. If the new codes are used to evaluate such old pipeline spans, considering all the before mentioned uncertainties in the input parameters, this would eventually lead to over conservative very low time to failures. The outcome will be that many spans need to be fixed immediately or should have failed already. Such a situation leads to a mistaken conclusion about the conservatism of the codes and not on the way they were applied.This paper discusses some of the challenges often seen with free spans during the operational phase. The objective of the paper is to demonstrate that for in-service pipelines the lack of reliable information about the free spans is the main source of commonly low life encountered and not the methodology used to evaluate the free span. Some of these challenges are discussed in detail and potential ways forward are outlined.Copyright © 2014 by ASME
R. D. Haun - One of the best experts on this subject based on the ideXlab platform.
-
The effect of residual Tension and free span-induced moments on vortex shedding of deep water pipelines
1994Co-Authors: H. S. Choi, R. D. HaunAbstract:Tensioned beam theory is used to calculate displacements and moments of free spanned portions of offshore pipelines. The Rayleigh method is implemented to calculate the fundamental frequency of the pipeline span under the effects of residual Tension and span-induced moments. This procedure is simple and yields a more accurate natural frequency of the pipe even with low residual Tension. The effect of the residual Tension and span-induced moments on the deep water pipeline was investigated. The benefit of controllable residual Lay Tension in the pipe was identified. This simple analytical procedure can be applied to offshore pipelines of any size and in any water depth.
Idan Mishal - One of the best experts on this subject based on the ideXlab platform.
-
Numerical analysis of offshore pipe-Lay subjected to environment-induced non-uniformly distributed follower loads
Applied Ocean Research, 2020Co-Authors: P Trapper, Idan MishalAbstract:Abstract The global pipeline configuration in installation is mainly governed by static Lay effects, which, besides pipeline material properties and geometry, primarily depend on its submerged gravity and horizontal Tension provided by the Laying vessel. These loads are insensitive to the pipeline deformation and preserve both their values and their directions as the pipeline deforms throughout the whole course of the installation. However, these static Lay effects may be significantly amplified by the environmental factors, primarily caused by astronomical ocean tides, such as water level variations and hydrodynamic currents. These factors may substantially affect pipeline configuration and significantly increase the internal forces. Moreover, the loads caused by the ocean currents are of a fundamentally different nature comparing to the gravity and the Lay Tension. They are nonuniformly distributed along the pipeline axis and change both their values and their directions following the nonlinear deformation of the pipeline throughout the course of the Laying process. This paper presents a feasible numerical method for a structural analysis of a pipeline static configuration in installation, subjected to non-uniformly distributed, position- and orientation-dependent loading and water level variations. The method considers the whole pipeline, which is partially suspended and partially laid-on a seabed, as a single continuous segment, and is valid for both S-Lay and J-Lay techniques. The numerical solution adopts finite difference discretization of the pipeline, and proceeds sequentially in an incremental way, following the actual pipe-Lay process. At each length increment a new consequent equilibrium configuration is being assessed by consistent minimization of the updated total potential energy, which allows for considering follower loads, which change both their values and their directions following the nonlinear deformation of the pipeline. Representative parametric study is conducted to demonstrate the feasibility of the method. Considered the effects of a power-law current velocity depth-varying profile and water level variations. The method compared to Abaqus/AQUA and its convergence is validated through finite difference grid refinement. The proposed technique presents a less time-consuming alternative to the available special-purpose commercial software that imposes the use of cumbersome Graphical User Interface for a model definition and a result processing.